(1) Field of the Invention
The present invention generally relates to a projection display apparatus and more particularly to a projection display apparatus using a liquid crystal light bulb.
(2) Description of the Related Art
It is preferable that a picture projected on a screen by a projection display unit is as bright as possible and the whole surface of the picture has a uniform brightness.
A conventional projection display apparatus is shown in FIG. 1. Referring to FIG. 1, a projection display apparatus 10 has a light source unit 12, a concentrator lens 13, a liquid crystal light bulb 14 and a projection lens 15. The light source unit 12 is formed of a metal halide lamp 12a (250 watts) and a parabolic reflector 12b. The liquid crystal light bulb 14 is a rectangular plate having a diagonal dimension of 3.2 inches. The liquid crystal light bulb 14 forms a picture thereon. Projection light 16 from the light source unit 12 is concentrated on the liquid crystal light bulb 14 by the concentrator lens 13. The projection light 16 is specially modulated by the picture formed on the liquid crystal light bulb 14. A projection light 16 A which is spatially modulated passes through the projection lens 15 and is projected on a screen 20. As a result, an enlarged picture 21 is displayed on the screen 20.
The light source unit 12 has a structure in which the metal halide lamp 12a is surrounded by the parabolic reflector 12b. Thus, an illuminance distribution in which an illuminance decreases at positions displaced from an optical axis 11 is formed on the liquid crystal light bulb 14. Further, the transmittance of the projection lens 15 decreases at positions displaced from the optical axis 11. As a result, in the illuminance distribution of the picture 21 on the screen 20, as indicated by a curve I in FIG. 1, an illuminance in a fringe area of the picture 21 is approximately half as bright as an illuminance in a center area of the picture 21. Thus, the picture 21 on the screen does not have a high quality.